U.S. Pat. No. 4,690,981, granted Sept. 1, 1987 to Statz, discloses ionomers of ethylene, unsaturated carboxylic acid and a softening comonomer that can be blended with nylon to produce a toughened thermoplastic. Statz's invention differs from the present invention in the amount of ionomer used. Statz discloses levels of ionomer greater than or equal to 30 weight percent; the composition of the present invention discloses ionomer from 10-25 weight percent. No freedom from mold deposit is disclosed in Statz.
U.S. Pat. No. 4,174,358, granted Nov. 13, 1979 to Epstein, discloses a toughened multi-phase thermoplastic composition containing 60-99 weight percent of a polyamide matrix resin and 1-40 weight percent of a toughener. Among the tougheners disclosed in Epstein are several ionomers. The ionomers specifcally disclosed and exemplified in Epstein are chemically different from those disclosed in the present invention. Further, the compositions of the present invention are superior to the ionomer toughened compositions exemplified by Epstein; the compositions of the present invention have freedom from mold deposit and a better combination of toughness and stiffness.
U.S. Pat. No. 4,346,194, granted Aug. 24, 1982 to Roura, discloses a polyamide molding material having good impact strength at low temperature and comprising a 60-90 weight percent blend of nylon 66 (20-80 weight percent); nylon 6 (80-20 weight percent); and a toughening copolymer (3-40 weight percent). Roura shows that blends of nylon 66/6 have synergism with respect to toughness; however, the toughening copolymer is completely different than that used in the present invention. Furthermore, Roura is only concerned with good impact strength at low temperature, and makes no reference to flexural modulus and percent elongation.
U.S. Pat. No. 3,845,163, granted Oct. 29, 1974 to Murch, discloses from 60-85 weight percent of polyamide and from 15-40 weight percent of an ionomer, the composition having improved weld-line toughness. The compositions of the present invention contain a copolymer of three or more substituents, while no disclosure of such an ionic copolymer is made in the Murch reference. No mention is made of freedom from mold deposit in Murch.